1. Field of the Art
This invention relates to an inverter of the polyphase configuration including a plurality of unit inverters connected in parallel with a common d.c. power source.
2. Prior Art
For the system to obtain an alternating current from a d.c. power source, there is known a system to connect a plurality of inverters serving as unit inverters in parallel with a single d.c. power source to operate these inverters as they being out of phase with each other to synthesize their respective outputs, thus to provide a sine wave a.c. output. Such a system can reduce harmonics to much extent by synthesis of outputs of the plurality of inverters as compared to the system of individually operating inverters. Since many harmonics are included in the input current of the unit inverters, a filter circuit using a capacitor is inserted in the input. A fuse for cutting a current off at the time of short circuit of the capacitor is inserted in series with the capacitor. In addition, a reactor for protection coordination of the fuse is provided. Since the capacitor and the reactor exist as just described above, a resonance circuit is constituted.
If the resonance frequency of the resonance circuit is in correspondence with any frequency of harmonics included in the input current, an overcurrent is to flow in the resonance circuit. Thus, it is required to increase the rated capacity of the reactor or the capacitor, etc. by taking such an overcurrent into consideration. As a result, the filter circuit component becomes large in dimension accordingly and also becomes costly.